Little is known of Mould's early life, such as whether she had any brothers or sisters. Said to have the gift of Second Sight, she was accepted as a Wendron Witch.
One day when Silas Heap was in the Forest, he came across Morwenna Mould. She had been surrounded by wolverines, and in her haste, had accidentally Frozen herself. Silas saved her, and waited with her until she DeFrosted. During that time, he told her about his son, Simon, and his wife, Sarah. Morwenna was very grateful for Silas for saving her life. In return, she offered him anything he wanted. Silas requested that the Wendron Witch stop preying on the inhabitants of the Castle. The two remained friends for some time.
Some time after those events, Morwenna became Witch Mother. She was then in charge of the Forest Coven.
The Wendron Witch took in three of the Heap boys in the Forest, a grouping that eventually became known as Camp Heap. A strange individual known only as Wolf Boy was also part of this grouping. When Septimus and Nicko came to Camp Heap looking for Wolf Boy, they visited Mould. She told them that she foresaw troubles ahead, and that there were three things they must know:
- They will find their sister, Jenna, at the Port.
- A tall, dark man, a stranger to some but not all, will also search for Jenna at the Port.
- They must not go to the circus.
Despite her promise to Silas, Mould could not resist the opportunity to try to snatch Jenna, as the capture and induction of a Princess-in-Waiting brought great status to a Witch Coven. Mould enlisted the help of a Castle cat, Binkie, as her familiar, and came up with a plan for the abduction. She engaged in the ancient art of FootFollowing in order to tail Jenna directly via her footprints. After great difficulties, she succeeded in capturing Jenna, but was thwarted when Jenna's biological father, Milo Banda, released Jenna using a powerful Reverse.